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Helically coiled steam generator is an essential part of current generation small modular reactors like NuScale due to its compactness and high heat transfer area. Instabilities due to boiling water inside helically coiled tubes is an important research question due to its im-portance for the steady-state operation of the plant. This study presents an experimental in-vestigation of two-phase boiling instabilities inside helically coiled tubes. Five experiments were carried out with different thermal power, and mass flow rates to understand flow be-haviour under different system conditions. It is found that thermal oscillation inside the tube increases with the power step and tube length while decreasing with the mass flow rate. The thermal oscillation period also increases with a higher power step. A semi-empirical corre-lation based on experimental data is developed. The overall heat transfer coefficient is cal-culated theoretically using the Chen correlation and later compared with the experimental value. Both experimental and theoretical value of the heat transfer coefficient agrees well. Uparjalnik s spiralnimi cevmi je zaradi svoje kompaktnosti in velike površine za prenos toplote osnovna komponenta trenutne generacije majhnih modularnih reaktorjev kot je NuScale. Nestabilnost vrenja v spiralnih ceveh je pomembno vprašanje, saj se ji je potrebno v stacionarnih razmerah izogniti. Ta magistrska nalogaa predstavlja eksperimentalno raziskavo nestabilnosti dvofaznega vrenja znotraj spiralno zvitih cevi. Izvedenih je bilo pet poskusov z različno toplotno močjo in masnimi pretoki, da bi razumeli obnašanje pretoka skozi uparjalnik v različnih pogojih. Ugotovljeno je bilo, da temperaturna nihanja znotraj cevi naraščajo ob stopničastih prirastkih moči in z dolžino cevi, medtem ko se zmanjšujejo z masnim pretokom. Tudi nihajni čas se poveča ob večjih stopničastih prirastkih moči. Razvita je semiempirična korelacija na podlagi eksperimentalnih podatkov. Skupni koeficient toplotne prestopnosti izračunamo teoretično z uporabo Chenove korelacije in jo primerjamo z eksperimentalno vrednostjo. Eksperimentalna in teoretična vrednost koeficienta toplotnega prestopnosti se dobro ujemata. |
